1. Field of the Invention
The present invention relates to a method for treating a lignocellulose biomass in order to dissolve the lignin therein, while the cellulose does not dissolve. The cellulose pulp obtained can be used to produce glucose. In addition the lignin can be isolated for subsequent use in the renewable chemical industry as a source for aromatic platform chemicals.
2. Description of Related Art
Biofuels can be generated by fermenting sugars to produce bioethanol. Currently biofuels are generally derived from food resources. This leads to several problems as there is competition with the food supply for the raw materials; the yield is low per unit area of land and a high energy input is required to grow the crops. It is possible to produce the sugar required by hydrolysing starch, or the sucrose produced by plants like sugar cane or sugar beet can be used. The problems could be alleviated if the woody part of plants from agricultural residues, forestry residues and energy crops could be used.
The woody or structural parts of the plant have evolved to withstand degradation. They are made up of mainly cellulose, hemicellulose and lignin. Pretreatment of the material is required in order to break up the structure. Generally pretreatment involves one or more of the following: removing the hemicelluose; modifying and solubilising the lignin; hydrolysing the hemicellulose-lignin linkages; and reducing the crystallinity of the cellulose fibres. This makes the celullose more accessible to enzymes, and also removes potential inhibitors of the fermentation stage.
Several pretreatment strategies have been previously described. These include steam explosion, catalysis with dilute acid or a base, ammonia fibre expansion, Organosolv pulping and biological pretreatment. All of these processes have their disadvantages. Pretreatment with ionic liquids has also been described. Ionic liquids (ILs) are salts that are liquid at the temperature of interest. The combination of anions and cations can be chosen to match the particular application required.
WO10/0056790 describes the use of substantially water free ILs to dissolve biomass which can then be separated using various solvents. WO08/090155 and WO08/090156 both describe the use of ILs to dissolve all the biomass components e.g. the lignin, hemicellulose and cellulose. In these methods the cellulose is separated from the other components usually by adding a suitable solvent so that the cellulose precipitates out and can be separated. Two recent reports applying [MeSO4]− containing ionic liquids for biomass pretreatment concluded that the ionic liquid is not capable of enhancing the digestibility of neither maple wood nor corn cob.
WO2008/112291 describes the use of ionic liquids to pretreat a lignin containing biomass to increase the yield in a subsequent saccharification reaction. The IL is used to swell the biomass structure and not achieve any dissolution of the lignocellulose. Lignin can be recovered as a post-saccharification solid.
US2010-0081798 describes the use of ILs containing a polyatomic anion to solubilise lignocellulose. The cellulose dissolves in the IL.
WO2005/017252 discloses the use of ILs with an aromatic anion to dissolve the lignin from biomass allowing the cellulosic fibres obtained to be further processed.